Chassis jig and structural repair

What a chassis jig is and what it's for

A chassis jig is a heavy-duty bench the car is clamped to by its anchor points. With a measuring system, it lets us compare the car's actual geometry with the dimensions published by the manufacturer. With pulling towers and chains, it lets us bring the structure back into place in a controlled way, without stressing the metal more than necessary.

Modern cars have a monocoque structure: the bodywork and chassis form a single unit. That's why an impact that looks like a panel job may have shifted a front chassis leg, a crossmember or a door frame.

Signs the structure may be affected

After a heavy knock, a few clues suggest the car should be checked on the jig even if it doesn't look serious from outside:

• Uneven gaps between bonnet, wings and doors.
• Doors or tailgate that are hard to shut or rattle.
• Cracks in the sealer or paint along inner joints.
• Outer panels that won't line up, even new ones.
• Creases in the metal away from the point of impact.

On the mountain roads of southern Tenerife, a car with altered geometry shouldn't just carry on as normal: if something seems wrong after a knock, bring it in as soon as you can.

How structural repair is done

First we remove the damaged outer panels and measure. With the data in front of us, we plan the pulls: direction, force and order. We pull gradually and measure again until the car is within tolerance. If a part can't be recovered, we cut it out and replace it following the procedure the manufacturer sets for that model.

When a structural part is replaced, it goes back on with the same type of joint it had from the factory. On steel bodies that's usually spot welding, with the welds well spaced so the metal doesn't overheat; aluminium parts are often joined by riveting combined with structural adhesive. Before joining, the flanges are flattened, the paint is cleaned off the joint area and the inner faces of the metal are protected, because they can't be reached afterwards. Aluminium must also be kept away from steel residue to avoid galvanic corrosion.

Once the structure is right, we refit the outer panels, adjust the gaps and move on to paint. We seal the joints as they came from the factory and apply cavity wax inside the hollow sections, so the repaired area resists damp and salt air just like the rest of the car.

This type of repair usually follows an insurance claim. If so, we deal with your insurer: see our insurer liaison service and our guide to the loss assessment. If there's no insurance involved, we give you a written estimate before we start.